Audio signal processing apparatus

ABSTRACT

An audio signal encoding apparatus includes a device for compressing multiple-channel digital audio signals into compression-resultant multiple-channel signals respectively. The multiple-channel digital audio signals relate to a sampling frequency and a quantization bit number. The compression-resultant multiple-channel signals, a signal representative of the sampling frequency, and a signal representative of the quantization bit number are formatted into a formatting-resultant signal. The formatting-resultant signal contains a sub packet and a sync information portion. The sub packet contains at least portions of the compression-resultant multiple-channel signals. The sync information portion contains the signal representative of the sampling frequency and the signal representative of the quantization bit number.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an audio signal encoding apparatus. Thisinvention also relates to an optical recording medium. In addition, thisinvention relates to an audio signal decoding apparatus. Furthermore,this invention relates to a method of transmitting an audio signal, anda transmission medium.

2. Description of the Related Art

Highly efficient encoding of an audio signal includes a step ofcompressing the audio signal. Highly efficient encoding techniques areclassified into two types; the lossy encoding techniques and thelossless encoding techniques. Among the lossy encoding techniques, the“acoustic encoding” is well known as a technique which renders the datadeterioration acoustically undetectable. On the other hand, according tothe lossless encoding and decoding techniques, the recovered data areexactly the same as the original data.

In general, a sampled or uniformly quantized audio signal hassignificant redundancy. During the encoding of such an audio signal, thedegree of the compression of the audio signal rises as redundancy ismore effectively removed therefrom.

SUMMARY OF THE INVENTION

It is a first object of this invention to provide an improved audiosignal encoding apparatus.

It is a second object of this invention to provide an improved opticalrecording medium.

It is a third object of this invention to provide an improved audiosignal decoding apparatus.

It is a fourth object of this invention to provide an improved method oftransmitting an audio signal.

It is a fifth object of this invention to provide an improvedtransmission medium.

A first aspect of this invention provides an audio signal encodingapparatus comprising means for compressing multiple-channel digitalaudio signals into compression-resultant multiple-channel signalsrespectively, the multiple-channel digital audio signals relating to asampling frequency and a quantization bit number; and means forformatting the compression-resultant multiple-channel signals, a signalrepresentative of the sampling frequency, and a signal representative ofthe quantization bit number into a formatting-resultant signal, theformatting-resultant signal containing a sub packet and a syncinformation portion, the sub packet containing at least portions of thecompression-resultant multiple-channel signals, the sync informationportion containing the signal representative of the sampling frequencyand the signal representative of the quantization bit number.

A second aspect of this invention provides an optical recording mediumstoring a formatting-resultant signal containing a sub packet and a syncinformation portion, the sub packet containing at least portions ofcompression-resultant multiple-channel signals which result fromcompressing multiple-channel digital audio signals respectively, thesync information portion containing a signal representative of asampling frequency related to the multiple-channel digital audio signalsand a signal representative of a quantization bit number related to themultiple-channel digital audio signals.

A third aspect of this invention provides an audio signal decodingapparatus comprising means for separating a formatting-resultant signalinto a sub packet and a sync information portion; means for extractingcompression-resultant multiple-channel signals from the sub packet;means for expanding the extracted compression-resultant multiple-channelsignals into multiple-channel digital audio signals respectively; meansfor extracting a signal representative of a sampling frequency and asignal representative of a quantization bit number from the syncinformation portion; and means. for converting the multiple-channeldigital audio signals into analog audio signals in response to thesignal representative of the sampling frequency and the signalrepresentative of the quantization bit number.

A fourth aspect of this invention provides a method of transmitting anaudio signal. The method comprises the steps of compressingmultiple-channel digital audio signals into compression-resultantmultiple-channel signals respectively, the multiple-channel digitalaudio signals relating to a sampling frequency and a quantization bitnumber; formatting the compression-resultant multiple-channel signals, asignal representative of the sampling frequency, and a signalrepresentative of the quantization bit number into aformatting-resultant signal, the formatting-resultant signal containinga sub packet and a sync information portion, the sub packet containingat least portions of the compression-resultant multiple-channel signals,the sync information portion containing the signal representative of thesampling frequency and the signal representative of the quantization bitnumber; and transmitting the formatting-resultant signal through acommunication line.

A fifth aspect of this invention provides an audio signal encodingapparatus comprising means for compressing multiple-channel digitalaudio signals into compression-resultant multiple-channel signalsrespectively; and means for formatting the compression-resultantmultiple-channel signals and an identifier into a formatting-resultantsignal, the formatting-resultant signal containing a sub packet and async information portion, the sub packet containing at least portions ofthe compression-resultant multiple-channel signals, the sync informationportion containing the identifier, the identifier representing thatsignals in the sub packet are compression-resultant signals.

A sixth aspect of this invention provides an optical recording mediumstoring a formatting-resultant signal containing a sub packet and a syncinformation portion, the sub packet containing at least portions ofcompression-resultant multiple-channel signals which result fromcompressing multiple-channel digital audio signals respectively, thesync information portion containing an identifier representing thatsignals in the sub packet are compression-resultant signals.

A seventh aspect of this invention provides an audio signal decodingapparatus comprising means for separating a formatting-resultant signalinto a sub packet and a sync information portion; means for extractingcompression-resultant multiple-channel signals from the sub packet;means for extracting an identifier from the sync information portion,the identifier representing that signals in the sub packet arecompression-resultant signals; and means for expanding the extractedcompression-resultant multiple-channel signals into multiple-channeldigital audio signals in response to the extracted identifier,respectively.

An eighth aspect of this invention provides a method of transmitting anaudio signal. The method comprises the steps of compressingmultiple-channel digital audio signals into compression-resultantmultiple-channel signals respectively; formatting thecompression-resultant multiple-channel signals and an identifier into aformatting-resultant signal, the formatting-resultant signal containinga sub packet and a sync information portion, the sub packet containingat least portions of the compression-resultant multiple-channel signals,the sync information portion containing the identifier, the identifierrepresenting that signals in the sub packet are compression-resultantsignals; and transmitting the formatting-resultant signal through acommunication line.

A ninth aspect of this invention provides a DVD-audio disc storing anaudio pack loaded with a formatting-resultant signal containing a subpacket and a sync information portion, the sub packet containing atleast portions of compression-resultant multiple-channel signals whichresult from compressing multiple-channel digital audio signalsrespectively, the sync information portion containing a signalrepresentative of a sampling frequency related to the multiple-channeldigital audio signals and a signal representative of a quantization bitnumber related to the multiple-channel digital audio signals.

A tenth aspect of this invention is based on the third aspect thereof,and provides an audio signal decoding apparatus further comprising meansfor separating an audio packet from an audio pack, the audio packetcontaining said formatting-resultant signal.

An eleventh aspect of this invention provides a DVD-audio disc storingan audio pack loaded with a formatting-resultant signal containing a subpacket and a sync information portion, the sub packet containing atleast portions of compression-resultant multiple-channel signals whichresult from compressing multiple-channel digital audio signalsrespectively, the sync information portion containing an identifierrepresenting that signals in the sub packet are compression-resultantsignals.

A twelfth aspect of this invention is based on the seventh aspectthereof, and provides an audio signal decoding apparatus furthercomprising means for separating an audio packet from an audio pack, theaudio packet containing said formatting-resultant signal.

A thirteenth aspect of this invention provides a transmission medium fortransmitting data being in a format and being made by a methodcomprising the steps of compressing multiple-channel digital audiosignals into compression-resultant multiple-channel signalsrespectively; and formatting the compression-resultant multiple-channelsignals and an identifier into a formatting-resultant signal, theformatting-resultant signal containing a sub packet and a syncinformation portion, the sub packet containing at least portions of thecompression-resultant multiple-channel signals, the sync informationportion containing the identifier, the identifier representing thatsignals in the sub packet are compression-resultant signals.

A fourteenth aspect of this invention provides a transmission medium fortransmitting a formatting-resultant signal containing a sub packet and async information portion, the sub packet containing at least portions ofcompression-resultant multiple-channel signals which result fromcompressing multiple-channel digital audio signals respectively, thesync information portion containing an identifier representing thatsignals in the sub packet are compression-resultant signals.

A fifteenth aspect of this invention provides a transmission medium fortransmitting a formatting-resultant signal which is decoded by an audiosignal decoding apparatus comprising means for separating theformatting-resultant signal into a sub packet and a sync informationportion; means for extracting compression-resultant multiple-channelsignals from the sub packet; means for extracting an identifier from thesync information portion, the identifier representing that signals inthe sub packet are compression-resultant signals; and means forexpanding the extracted compression-resultant multiple-channel signalsinto multiple-channel digital audio signals in response to the extractedidentifier, respectively.

A sixteenth aspect of this invention provides a transmission medium fortransmitting an audio signal by a method comprising the steps ofcompressing multiple-channel digital audio signals intocompression-resultant multiple-channel signals respectively; formattingthe compression-resultant multiple-channel signals and an identifierinto a formatting-resultant signal, the formatting-resultant signalcontaining a sub packet and a sync information portion, the sub packetcontaining at least portions of the compression-resultantmultiple-channel signals, the sync information portion containing theidentifier, the identifier representing that signals in the sub packetare compression-resultant signals; and transmitting theformatting-resultant signal through a communication line.

A seventeenth aspect of this invention provides a transmission mediumfor transmitting data being in a format and being made by an audiosignal encoding apparatus comprising means for compressingmultiple-channel digital audio signals into compression-resultantmultiple-channel signals respectively, the multiple-channel digitalaudio signals relating to a sampling frequency and a quantization bitnumber; and means for formatting the compression-resultantmultiple-channel signals, a signal representative of the samplingfrequency, and a signal representative of the quantization bit numberinto a formatting-resultant signal, the formatting-resultant signalcontaining a sub packet and a sync information portion, the sub packetcontaining at least portions of the compression-resultantmultiple-channel signals, the sync information portion containing thesignal representative of the sampling frequency and the signalrepresentative of the quantization bit number.

An eighteenth aspect of this invention provides a transmission mediumfor transmitting a formatting-resultant signal containing a sub packetand a sync information portion, the sub packet containing at leastportions of compression-resultant multiple-channel signals which resultfrom compressing multiple-channel digital audio signals respectively,the sync information portion containing a signal representative of asampling frequency related to the multiple-channel digital audio signalsand a signal representative of a quantization bit number related to themultiple-channel digital audio signals.

A nineteenth aspect of this invention provides a transmission medium fortransmitting a formatting-resultant signal which is decoded by an audiosignal decoding apparatus comprising means for separating aformatting-resultant signal into a sub packet and a sync informationportion; means for extracting compression-resultant multiple-channelsignals from the sub packet; means for expanding the extractedcompression-resultant multiple-channel signals into multiple-channeldigital audio signals respectively; means for extracting a signalrepresentative of a sampling frequency and a signal representative of aquantization bit number from the sync information portion; and means forconverting the multiple-channel digital audio signals into analog audiosignals in response to the signal representative of the samplingfrequency and the signal representative of the quantization bit number.

A twentieth aspect of this invention provides a transmission medium fortransmitting an audio signal by a method comprising the steps ofcompressing multiple-channel digital audio signals intocompression-resultant multiple-channel signals respectively, themultiple-channel digital audio signals relating to a sampling frequencyand a quantization bit number; formatting the compression-resultantmultiple-channel signals, a signal representative of the samplingfrequency, and a signal representative of the quantization bit numberinto a formatting-resultant signal, the formatting-resultant signalcontaining a sub packet and a sync information portion, the sub packetcontaining at least portions of the compression-resultantmultiple-channel signals, the sync information portion containing thesignal representative of the sampling frequency and the signalrepresentative of the quantization bit number; and transmitting theformatting-resultant signal through a communication line.

A twenty-first aspect of this invention provides an audio signalencoding apparatus comprising an fs conversion circuit for equalizingsampling frequencies of first multiple-channel digital audio signals toconvert a set of the first multiple-channel digital audio signals into aset of second multiple-channel digital audio signals; means forcompressing the second multiple-channel digital audio signals intocompression-resultant multiple-channel signals respectively, the secondmultiple-channel digital audio signals relating to a sampling frequencyand a quantization bit number; and means for formatting thecompression-resultant multiple-channel signals, a signal representativeof the sampling frequency, and a signal representative of thequantization bit number into a formatting-resultant signal, theformatting-resultant signal containing a sub packet and a syncinformation portion, the sub packet containing at least portions of thecompression-resultant multiple-channel signals, the sync informationportion containing the signal representative of the sampling frequencyand the signal representative of the quantization bit number.

A twenty-second aspect of this invention provides an optical recordingmedium storing a formatting-resultant signal containing a sub packet anda sync information portion, the sub packet containing at least portionsof compression-resultant multiple-channel signals which result fromequalizing sampling frequencies of multiple-channel digital audiosignals and then compressing the multiple-channel digital audio signalsrespectively, the sync information portion containing a signalrepresentative of a sampling frequency related to the multiple-channeldigital audio signals and a signal representative of a quantization bitnumber related to the multiple-channel digital audio signals.

A twenty-third aspect of this invention provides a method oftransmitting an audio signal, comprising the steps of equalizingsampling frequencies of first multiple-channel digital audio signals toconvert a set of the first multiple-channel digital audio signals into aset of second multiple-channel digital audio signals; compressing thesecond multiple-channel digital audio signals into compression-resultantmultiple-channel signals respectively, the second multiple-channeldigital audio signals relating to a sampling frequency and aquantization bit number; formatting the compression-resultantmultiple-channel signals, a signal representative of the samplingfrequency, and a signal representative of the quantization bit numberinto a formatting-resultant signal, the formatting-resultant signalcontaining a sub packet and a sync information portion, the sub packetcontaining at least portions of the compression-resultantmultiple-channel signals, the sync information portion containing thesignal representative of the sampling frequency and the signalrepresentative of the quantization bit number; and transmitting theformatting-resultant signal through a communication line.

A twenty-fourth aspect of this invention provides a transmission mediumfor transmitting an audio signal by a method comprising the steps ofequalizing sampling frequencies of first multiple-channel digital audiosignals to convert a set of the first multiple-channel digital audiosignals into a set of second multiple-channel digital audio signals;compressing the second multiple-channel digital audio signals intocompression-resultant multiple-channel signals respectively, the secondmultiple-channel digital audio signals relating to a sampling frequencyand a quantization bit number; formatting the compression-resultantmultiple-channel signals, a signal representative of the samplingfrequency, and a signal representative of the quantization bit numberinto a formatting-resultant signal, the formatting-resultant signalcontaining a sub packet and a sync information portion, the sub packetcontaining at least portions of the compression-resultantmultiple-channel signals, the sync information portion containing thesignal representative of the sampling frequency and the signalrepresentative of the quantization bit number; and transmitting theformatting-resultant signal through a communication line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system including an audio signal encodingapparatus and an audio signal decoding apparatus according to a firstembodiment of this invention.

FIG. 2 is a block diagram of an encoder in FIG. 1.

FIG. 3 is a block diagram of a prediction circuit in FIG. 2.

FIG. 4 is a diagram of a structure of an audio pack.

FIG. 5 is a diagram of the structure of the audio pack.

FIG. 6 is a diagram of a structure of an audio packet in FIG. 5.

FIG. 7 is a block diagram of a decoder in FIG. 1.

FIG. 8 is a time-domain diagram of the amount of data in an inputbuffer, a SCR signal, and a DTS signal.

FIG. 9 is a time-domain diagram of a PTS signal.

FIG. 10 is a time-domain diagram of a sequence of access units and asequence of presentation units.

FIG. 11 is a block diagram of a system according to a second embodimentof this invention.

FIG. 12 is a flowchart of a segment of a control program for a packetingprocessor in FIG. 11.

FIG. 13 is a flowchart of a segment of a control program for ade-packeting processor in FIG. 11.

FIG. 14 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to afourth embodiment of this invention.

FIG. 15 is a block diagram of an audio signal encoding apparatus in asystem according to a fifth embodiment of this invention.

FIG. 16 is a block diagram of an audio signal decoding apparatus in thesystem according to the fifth embodiment of this invention.

FIG. 17 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to asixth embodiment of this invention.

FIG. 18 is a diagram of a structure of an audio packet used in a seventhembodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

With reference to FIG. 1, an audio signal encoding apparatus 100includes a mix and matrix circuit 110 and an encoder 120. The mix andmatrix circuit 110 is followed by the encoder 120. An audio signaldecoding apparatus 200 includes a decoder 130 and a mix and matrixcircuit 140. The decoder 130 is followed by the mix and matrix circuit140. The audio signal encoding apparatus 100 and the audio signaldecoding apparatus 200 are connected via a transmission line 250. Thetransmission line 250 includes a communication line or a communicationnetwork. Alternatively, the transmission line 250 may include acombination of a recording unit, a recording medium, and a reproducingunit. For example, the recording medium is a DVD-audio, another opticaldisc, or a magnetic disc.

The audio signal encoding apparatus 100 receives 6-channel input digitalaudio signals, that is, a left-front digital audio signal Lf, aright-front digital audio signal Rf, a center digital audio signal C, aleft-surround digital audio signal Ls, a right-surround digital audiosignal Rs, and a low-frequency-effect digital audio signal Lfe. Theleft-front digital audio signal Lf results from quantization of aleft-front analog audio signal at a predetermined sampling frequency fsand a predetermined quantization bit number Qb. The predeterminedsampling frequency fs is equal to, for example, 96 kHz or 192 kHz. Thepredetermined quantization bit number Qb is equal to, for example, 20 or24. Similarly, each of the right-front digital audio signal Rf, thecenter digital audio signal C, the left-surround digital audio signalLs, the right-surround digital audio signal Rs, and thelow-frequency-effect digital audio signal Lfe results from quantizationof a corresponding analog audio signal at the predetermined samplingfrequency and the predetermined quantization bit number. The audiosignal encoding apparatus 100 encodes the 6-channel input digital audiosignals into a bit stream which is an encoding-resultant digital audiosignal. The audio signal encoding apparatus 100 outputs theencoding-resultant digital audio signal to the transmission line 250.

The encoding-resultant digital audio signal is propagated to the audiosignal decoding apparatus 200 via the transmission line 250. In the casewhere the transmission line 250 includes the combination of therecording unit, the recording medium, and the reproducing unit, theencoding-resultant digital audio signal is recorded on the recordingmedium via the recording unit while the encoding-resultant digital audiosignal is read out from the recording medium via the reproducing unit.The audio signal decoding apparatus 200 decodes the encoding-resultantdigital audio signal into the original 6-channel digital audio signals,that is, the original left-front digital audio signal Lf, the originalright-front digital audio signal Rf, the original center digital audiosignal C, the original left-surround digital audio signal Ls, theoriginal right-surround digital audio signal Rs, and the originallow-frequency-effect digital audio signal Lfe. In other words, the audiosignal decoding apparatus 200 recovers the 6-channel original digitalaudio signals (the 6-channel input digital audio signals). The audiosignal decoding apparatus 200 outputs the 6-channel recovered digitalaudio signals to an external apparatus.

The mix and matrix circuit 110 in the audio signal encoding apparatus100 receives the 6-channel input digital audio signals, that is, theleft-front digital audio signal Lf, the right-front digital audio signalRf, the center digital audio signal C, the left-surround digital audiosignal Ls, the right-surround digital audio signal Rs, and thelow-frequency-effect digital audio signal Lfe. The mix and matrixcircuit 110 includes an adder which adds the left-front digital audiosignal Lf and the right-front digital audio signal Rf into a firstcalculation-result signal S1. The first calculation-result signal S1 isgiven by the relation as “S1=Lf+Rf”. The first calculation-result signalis also denoted by Lf+Rf. The first calculation-result signal S1 is aPCM signal. The mix and matrix circuit 110 includes a subtracter whichsubtracts the right-front digital audio signal Rf from the left-frontdigital audio signal Lf to generate a second calculation-result signalS2. The second calculation-result signal S2 is given by the relation as“S2=Lf−Rf”. The second calculation-result signal is also denoted byLf−Rf. The second calculation-result signal S2 is a PCM signal. The mixand matrix circuit 110 includes a combination of an adder, a ½ divider,and a subtracter which processes the center digital audio signal C, theleft-surround digital audio signal Ls, and the right-surround digitalaudio signal Rs into a third calculation-result signal S3. The thirdcalculation-result signal S3 is given by the relation as

${\;^{``}S\; 3} = {C - {\left( \frac{{Ls} + {Rs}}{2} \right)^{''}.}}$The third calculation-result signal is also denoted by C−(Ls+Rs)/2. Thethird calculation-result signal S3 is a PCM signal. The mix and matrixcircuit 110 includes an adder which adds the left-surround digital audiosignal Ls and the right-surround digital audio signal Rs into a fourthcalculation-result signal S4. The fourth calculation-result signal S4 isgiven by the relation as “S4=Ls+Rs”. The fourth calculation-resultsignal is also denoted by Ls+Rs. The fourth calculation-result signal S4is a PCM signal. The mix and matrix circuit 110 includes a subtracterwhich subtracts the right-surround digital audio signal Rs from theleft-surround digital audio signal Ls to generate a fifthcalculation-result signal S5. The fifth calculation-result signal S5 isgiven by the relation as “S5=Ls−Rs”. The fifth calculation-result signalS5 is also denoted by Ls−Rs. The fifth calculation-result signal S5 is aPCM signal. The mix and matrix circuit 110 includes a combination of amultiplier and a subtracter which processes the center digital audiosignal C and the low-frequency-effect digital audio signal Lfe into asixth calculation-result signal S6. The sixth calculation-result signalS6 is given by the relation as “S6=Lfe−a×C” where “×” denotes a productoperator or a multiplication operator, and “a” denotes a fixed orvariable coefficient in the range between 0 and 1. The sixthcalculation-result signal is also denoted by Lfe−a×C. The sixthcalculation-result signal S6 is a PCM signal. A signal representative ofthe coefficient “a” is applied to the mix and matrix circuit 110 from anexternal.

In the case where 6-channel input digital audio signals are different insampling frequency and quantization bit number, an up-sampling device(not shown) precedes the mix and matrix circuit 110. The up-samplingdevice processes digital audio signals among the 6-channel input digitalaudio signals which relate to a lower sampling frequency and a lowerquantization bit number. Specifically, the up-sampling device convertssuch digital audio signals into corresponding digital audio signalswhich are equal in sampling frequency and quantization bit number to theother digital audio signals among the 6-channel input digital audiosignals. Accordingly, the 6-channel digital audio signals which resultfrom the processing by the up-sampling device are equal to each other insampling frequency and quantization bit number. The processing-resultant6-channel digital audio signals are fed to the mix and matrix circuit110 as 6-channel input digital audio signals.

In the audio signal encoding apparatus 100, the mix and matrix circuit110 outputs the first, second, third, fourth, fifth, and sixthcalculation-result signals S1, S2, S3, S4, S5, and S6 to the encoder120. The device 120 encodes the calculation-result signals S1-S6 into abit stream which is an encoding-resultant digital audio signal. Theencoder 120 outputs the encoding-resultant digital audio signal to thetransmission line 250.

As shown in FIG. 2, the encoder 120 includes a buffer (a memory) 10. Asequence of samples of each of the calculation-result signals S1, S2,S3, S4, S5, and S6 is applied to the buffer 10. The calculation-resultsignals S1-S6 are stored into the buffer 10 frame by frame. Every frameis composed of a predetermined number of successive samples. Samples ofthe calculation-result signal S1, that is, the calculation-result signalLf+Rf, are sequentially transmitted from the buffer 10 to a predictioncircuit 13D1. Samples of the calculation-result signal S2, that is, thecalculation-result signal Lf−Rf, are sequentially transmitted from thebuffer 10 to a prediction circuit 13D2. Samples of thecalculation-result signal S3, that is, the calculation-result signalC−(Ls+Rs)/2, are sequentially transmitted from the buffer 10 to aprediction circuit 13D3. Samples of the calculation-result signal S4,that is, the calculation-result signal Ls+Rs, are sequentiallytransmitted from the buffer 10 to a prediction circuit 13D4. Samples ofthe calculation-result signal S5, that is, the calculation-result signalLs−Rs, are sequentially transmitted from the buffer 10 to a predictioncircuit 13D5. Samples of the calculation-result signal S6, that is, thecalculation-result signal Lfe−a×C, are sequentially transmitted from thebuffer 10 to a prediction circuit 13D6. For every frame, the firstsamples of the respective calculation-result signals S1-S6 aretransmitted from the buffer 10 to a formatting circuit 19.

The prediction circuits 13D1-13D6 are similar to each other.Accordingly, only the prediction circuit 13D1 will be explained indetail hereinafter. As shown in FIG. 3, the prediction circuit 13D1includes predictors 13 a-1, 13 a-2, . . . , and 13 a-n, and subtracters13 b-1, 13 b-2, . . . , and 13 b-n, where “n” denotes a predeterminednatural number equal to or greater than 2. The predictors 13 a-1, 13a-2, . . . , and 13 a-n receive every sample of the calculation-resultsignal S1 (that is, the calculation-result signal Lf+Rf) from the buffer10. Also, the subtracters 13 b-1, 13 b-2, . . . , and 13 b-n receiveevery sample of the calculation-result signal S1 from the buffer 10. Thepredictors 13 a-1, 13 a-2, . . . , and 13 a-n have different predictioncharacteristics, respectively. Specifically, the predictors 13 a-1, 13a-2, . . . , and 13 a-n are different from each other in predictioncoefficients. Each of the predictors 13 a-1, 13 a-2, and 13 a-n predictsa current sample of the calculation-result signal S1 from precedingsamples thereof in response to the related prediction coefficients.Thus, the predictors 13 a-1, 13 a-2, . . . , and 13 a-n generateprediction-result signals for the calculation-result signal S1 (that is,the calculation-result signal Lf+Rf) in response to the predictioncoefficients, respectively. The predictors 13 a-1, 13 a-2, . . . , and13 a-n output the prediction-result signals to the subtracters 13 b-1,13 b-2, . . . , and 13 b-n respectively. For every sample, each of thesubtracters 13 b-1, 13 b-2, . . . , and 13 b-n subtracts the relatedprediction-result signal from the calculation-result signal S1, andhence generates a signal representing the prediction error between theprediction-result signal and the calculation-result signal S1. Thesubtracters 13 b-1, 13 b-2, . . . , and 13 b-n output the respectiveprediction-error signals to a buffer and selector 14D1.

The prediction-error signals, that is, the output signals of thesubtracters 13 b-1, 13 b-2, . . . , and 13 b-n, are temporarily storedin a memory within the buffer and selector 14D1. A selection signal/DTS(decoding time stamp) generator 17 produces a first selection signal.The selection signal/DTS generator 17 outputs the first selection signalto the buffer and selector 14D1. The first selection signal is designedto select the smallest one from among the prediction-error signals inthe memory of the buffer and selector 14D1 as an output signal of anoptimum subtracter (an optimum predictor) for every sub-frame.Specifically, for every sub-frame, the selection signal/DTS generator 17searches the memory within the buffer and selector 14D1 for the smallestprediction-error signal. In more detail, for every sub-frame, the sumsof the values represented by samples of the respective prediction-errorsignals are calculated. The calculated sums are compared to determinethe smallest one which corresponds to the smallest prediction-errorsignal to be selected. The selection signal/DTS generator 17 enables thebuffer and selector 14D1 to output the smallest prediction-error signalfrom the memory to a packing circuit 18 as the selected (Lf+Rf)-relatedprediction-error signal for every sub-frame.

Every sub-frame is composed of a predetermined number of successivesamples. Several tens of successive sub-frames compose one frame. Forexample, 80 successive sub-frames compose one frame.

The prediction circuit 13D2 generates different prediction-error signalswith respect to the calculation-result signal S2, that is, thecalculation-result signal Lf−Rf. The prediction circuit 13D2 outputs theprediction-error signals to a buffer and selector 14D2. Theprediction-error signals are temporarily stored in a memory within thebuffer and selector 14D2. The selection signal/DTS generator 17 producesa second selection signal. The selection signal/DTS generator 17 outputsthe second selection signal to the buffer and selector 14D2. The secondselection signal is designed to select the smallest one from among theprediction-error signals in the memory of the buffer and selector 14D2as an output signal of an optimum subtracter (an optimum predictor) forevery sub-frame. Specifically, for every sub-frame, the selectionsignal/DTS generator 17 searches the memory within the buffer andselector 14D2 for the smallest prediction-error signal. In more detail,for every sub-frame, the sums of the values represented by samples ofthe respective prediction-error signals are calculated. The calculatedsums are compared to determine the smallest one which corresponds to thesmallest prediction-error signal to be selected. The selectionsignal/DTS generator 17 enables the buffer and selector 14D2 to outputthe smallest prediction-error signal from the memory to the packingcircuit 18 as the selected (Lf−Rf)-related prediction-error signal forevery sub-frame.

The prediction circuit 13D3 generates different prediction-error signalswith respect to the calculation-result signal S3, that is, thecalculation-result signal C−(Ls+Rs)/2. The prediction circuit 13D3outputs the prediction-error signals to a buffer and selector 14D3. Theprediction-error signals are temporarily stored in a memory within thebuffer and selector 14D3. The selection signal/DTS generator 17 producesa third selection signal. The selection signal/DTS generator 17 outputsthe third selection signal to the buffer and selector 14D3. The thirdselection signal is designed to select the smallest one from among theprediction-error signals in the memory of the buffer and selector 14D3as an output signal of an optimum subtracter (an optimum predictor) forevery sub-frame. Specifically, for every sub-frame, the selectionsignal/DTS generator 17 searches the memory within the buffer andselector 14D3 for the smallest prediction-error signal. In more detail,for every sub-frame, the sums of the values represented by samples ofthe respective prediction-error signals are calculated. The calculatedsums are compared to determine the smallest one which corresponds to thesmallest prediction-error signal to be selected. The selectionsignal/DTS generator 17 enables the buffer and selector 14D3 to outputthe smallest prediction-error signal from the memory to the packingcircuit 18 as the selected (C−(Ls+Rs)/2)-related prediction-error signalfor every sub-frame.

The prediction circuit 13D4 generates different prediction-error signalswith respect to the calculation-result signal S4, that is, thecalculation-result signal Ls+Rs. The prediction circuit 13D4 outputs theprediction-error signals to a buffer and selector 14D4. Theprediction-error signals are temporarily stored in a memory within thebuffer and selector 14D4. The selection signal/DTS generator 17 producesa fourth selection signal. The selection signal/DTS generator 17 outputsthe fourth selection signal to the buffer and selector 14D4. The fourthselection signal is designed to select the smallest one from among theprediction-error signals in the memory of the buffer and selector 14D4as an output signal of an optimum subtracter (an optimum predictor) forevery sub-frame. Specifically, for every sub-frame, the selectionsignal/DTS generator 17 searches the memory within the buffer andselector 14D4 for the smallest prediction-error signal. In more detail,for every sub-frame, the sums of the values represented by samples ofthe respective prediction-error signals are calculated. The calculatedsums are compared to determine the smallest one which corresponds to thesmallest prediction-error signal to be selected. The selectionsignal/DTS generator 17 enables the buffer and selector 14D4 to outputthe smallest prediction-error signal from the memory to the packingcircuit 18 as the selected (Ls+Rs)-related prediction-error signal forevery sub-frame.

The prediction circuit 13D5 generates different prediction-error signalswith respect to the calculation-result signal S5, that is, thecalculation-result signal Ls−Rs. The prediction circuit 13D5 outputs theprediction-error signals to a buffer and selector 14D5. Theprediction-error signals are temporarily stored in a memory within thebuffer and selector 14D5. The selection signal/DTS generator 17 producesa fifth selection signal. The selection signal/DTS generator 17 outputsthe fifth selection signal to the buffer and selector 14D5. The fifthselection signal is designed to select the smallest one from among theprediction-error signals in the memory of the buffer and selector 14D5as an output signal of an optimum subtracter (an optimum predictor) forevery sub-frame. Specifically, for every sub-frame, the selectionsignal/DTS generator 17 searches the memory within the buffer andselector 14D5 for the smallest prediction-error signal. In more detail,for every sub-frame, the sums of the values represented by samples ofthe respective prediction-error signals are calculated. The calculatedsums are compared to determine the smallest one which corresponds to thesmallest prediction-error signal to be selected. The selectionsignal/DTS generator 17 enables the buffer and selector 14D5 to outputthe smallest prediction-error signal from the memory to the packingcircuit 18 as the selected (Ls−Rs)-related prediction-error signal forevery sub-frame.

The prediction circuit 13D6 generates different prediction-error signalswith respect to the calculation-result signal S6, that is, thecalculation-result signal Lfe−a×C. The prediction circuit 13D6 outputsthe prediction-error signals to a buffer and selector 14D6. Theprediction-error signals are temporarily stored in a memory within thebuffer and selector 14D6. The selection signal/DTS generator 17 producesa sixth selection signal. The selection signal/DTS generator 17 outputsthe sixth selection signal to the buffer and selector 14D6. The sixthselection signal is designed to select the smallest one from among theprediction-error signals in the memory of the buffer and selector 14D6as an output signal of an optimum subtracter (an optimum predictor) forevery sub-frame. Specifically, for every sub-frame, the selectionsignal/DTS generator 17 searches the memory within the buffer andselector 14D6 for the smallest prediction-error signal. In more detail,for every sub-frame, the sums of the values represented by samples ofthe respective prediction-error signals are calculated. The calculatedsums are compared to determine the smallest one which corresponds to thesmallest prediction-error signal to be selected. The selectionsignal/DTS generator 17 enables the buffer and selector 14D6 to outputthe smallest prediction-error signal from the memory to the packingcircuit 18 as the selected (Lfe−a×C)-related prediction-error signal forevery sub-frame.

The selection signal/DTS generator 17 produces a first flag representingthe maximum number among the numbers of effective bits in respectivesamples of the selected (Lf+Rf)-related prediction-error signal whichcompose one sub-frame. For every sub-frame, the selection signal/DTSgenerator 17 outputs the first flag to the packing circuit 18 and theformatting circuit 19 as an (Lf+Rf)-related bit-number flag.

The selection signal/DTS generator 17 produces a second flagrepresenting the maximum number among the numbers of effective bits inrespective samples of the selected (Lf−Rf)-related prediction-errorsignal which compose one sub-frame. For every sub-frame, the selectionsignal/DTS generator 17 outputs the second flag to the packing circuit18 and the formatting circuit 19 as an (Lf−Rf)-related bit-number flag.

The selection signal/DTS generator 17 produces a third flag representingthe maximum number among the numbers of effective bits in respectivesamples of the selected (C−(Ls+Rs)/2)-related prediction-error signalwhich compose one sub-frame. For every sub-frame, the selectionsignal/DTS generator 17 outputs the third flag to the packing circuit 18and the formatting circuit 19 as an (C−(Ls+Rs)/2)-related bit-numberflag.

The selection signal/DTS generator 17 produces a fourth flagrepresenting the maximum number among the numbers of effective bits inrespective samples of the selected (Ls+Rs)-related prediction-errorsignal which compose one sub-frame. For every sub-frame, the selectionsignal/DTS generator 17 outputs the fourth flag to the packing circuit18 and the formatting circuit 19 as an (Ls+Rs)-related bit-number flag.

The selection signal/DTS generator 17 produces a fifth flag representingthe maximum number among the numbers of effective bits in respectivesamples of the selected (Ls−Rs)-related prediction-error signal whichcompose one sub-frame. For every sub-frame, the selection signal/DTSgenerator 17 outputs the fifth flag to the packing circuit 18 and theformatting circuit 19 as an (Ls−Rs)-related bit-number flag.

The selection signal/DTS generator 17 produces a sixth flag representingthe maximum number among the numbers of effective bits in respectivesamples of the selected (Lfe−a×C)-related prediction-error signal whichcompose one sub-frame. For every sub-frame, the selection signal/DTSgenerator 17 outputs the sixth flag to the packing circuit 18 and theformatting circuit 19 as an (Lfe−a×C)-related bit-number flag.

For every sub-frame, the selection signal/DTS generator 1.7 produces aseventh flag representing the optimal predictor among the predictors 13a-1, 13 a-2, . . . , and 13 a-n in the prediction circuit 13D1, that is,the predictor causing the selected (Lf+Rf)-related prediction-errorsignal. The selection signal/DTS generator 17 outputs the seventh flagto the formatting circuit 19 as an (Lf+Rf)-related predictor-selectionflag.

For every sub-frame, the selection signal/DTS generator 17 produces aneighth flag representing the optimal predictor among the predictors inthe prediction circuit 13D2, that is, the predictor causing the selected(Lf−Rf)-related prediction-error signal. The selection signal/DTSgenerator 17 outputs the eighth flag to the formatting circuit 19 as an(Lf−Rf)-related predictor-selection flag.

For every sub-frame, the selection signal/DTS generator 17 produces aninth flag representing the optimal predictor among the predictors inthe prediction circuit 13D3, that is, the predictor causing the selected(C−(Ls+Rs)/2)-related prediction-error signal. The selection signal/DTSgenerator 17 outputs the ninth flag to the formatting circuit 19 as an(C−(Ls+Rs)/2)-related predictor-selection flag.

For every sub-frame, the selection signal/DTS generator 17 produces atenth flag representing the optimal predictor among the predictors inthe prediction circuit 13D4, that is, the predictor causing the selected(Ls+Rs)-related prediction-error signal. The selection signal/DTSgenerator 17 outputs the tenth flag to the formatting circuit 19 as an(Ls+Rs)-related predictor-selection flag.

For every sub-frame, the selection signal/DTS generator 17 produces aneleventh flag representing the optimal predictor among the predictors inthe prediction circuit 13D5, that is, the predictor causing the selected(Ls−Rs)-related prediction-error signal. The selection signal/DTSgenerator 17 outputs the eleventh flag to the formatting circuit 19 asan (Ls−Rs)-related predictor-selection flag.

For every sub-frame, the selection signal/DTS generator 17 produces atwelfth flag representing the optimal predictor among the predictors inthe prediction circuit 13D6, that is, the predictor causing the selected(Lfe−a×C)-related prediction-error signal. The selection signal/DTSgenerator 17 outputs the twelfth flag to the formatting circuit 19 as an(Lfe−a×C)-related predictor-selection flag.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (Lf+Rf)-related prediction-error signal into bits, the numberof which is equal to the maximum bit number represented by the(Lf+Rf)-related bit-number flag. Thus, the packing circuit 18 implementscompression of the selected (Lf+Rf)-related prediction-error signal. Thepacking circuit 18 outputs every packing-resultant sample of theselected (Lf+Rf)-related prediction-error signal to the formattingcircuit 19.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (Lf−Rf)-related prediction-error signal into bits, the numberof which is equal to the maximum bit number represented by the(Lf−Rf)-related bit-number flag. Thus, the packing circuit 18 implementscompression of the selected (Lf−Rf)-related prediction-error signal. Thepacking circuit 18 outputs every packing-resultant sample of theselected (Lf+Rf)-related prediction-error signal to the formattingcircuit 19.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (C−(Ls+Rs)/2)-related prediction-error signal into bits, thenumber of which is equal to the maximum bit number represented by the(C−(Ls+Rs)/2)-related bit-number flag. Thus, the packing circuit 18implements compression of the selected (C−(Ls+Rs)/2)-relatedprediction-error signal. The packing circuit 18 outputs everypacking-resultant sample of the selected (C−(Ls+Rs)/2)-relatedprediction-error signal to the formatting circuit 19.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (Ls+Rs)-related prediction-error signal into bits, the numberof which is equal to the maximum bit number represented by the(Ls+Rs)-related bit-number flag. Thus, the packing circuit 18 implementscompression of the selected (Ls+Rs)-related prediction-error signal. Thepacking circuit 18 outputs every packing-resultant sample of theselected (Ls+Rs)-related prediction-error signal to the formattingcircuit 19.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (Ls−Rs)-related prediction-error signal into bits, the numberof which is equal to the maximum bit number represented by the(Ls−Rs)-related bit-number flag. Thus, the packing circuit 18 implementscompression of the selected (Ls−Rs)-related prediction-error signal. Thepacking circuit 18 outputs every packing-resultant sample of theselected (Ls−Rs)-related prediction-error signal to the formattingcircuit 19.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (Lfe−a×C)-related prediction-error signal into bits, the numberof which is equal to the maximum bit number represented by the(Lfe−a×C)-related bit-number flag. Thus, the packing circuit 18implements compression of the selected (Lfe−a×C)-relatedprediction-error signal. The packing circuit 18 outputs everypacking-resultant sample of the selected (Lfe−a×C)-relatedprediction-error signal to the formatting circuit 19.

A signal generator 20 periodically produces a signal representing aframe header. The signal generator 20 outputs the frame-header signal tothe formatting circuit 19. A signal representing the coefficient “a” isapplied to the formatting circuit 19 from an external.

The formatting circuit 19 includes a multiplexer and a DVD-audioencoder. The multiplexer is followed by the DVD-audio encoder. Themultiplexer provides operation of the formatting circuit 19 which willbe indicated below.

The formatting circuit 19 receives the frame-header signal from thesignal generator 20 for every frame. The formatting circuit 19 receivesthe first sample of the calculation-result signal Lf+Rf and the firstsample of the calculation-result signal Lf−Rf from the buffer 10 forevery frame. The formatting circuit 19 receives the (Lf+Rf)-relatedpredictor-selection flag and the (Lf−Rf)-related predictor-selectionflag from the selection signal/DTS generator 17 for every sub-frame. Theformatting circuit 19 receives the (Lf+Rf)-related bit-number flag andthe (Lf−Rf)-related bit-number flag from the selection signal/DTSgenerator 17 for every sub-frame. The formatting circuit 19 receivesevery packing-resultant sample of the selected (Lf+Rf)-relatedprediction-error signal and every packing-resultant sample of theselected (Lf−Rf)-related prediction-error signal from the packingcircuit 18. The formatting circuit 19 multiplexes the received signalsand flags into a first sub bit stream BS0 on a time sharing basis. Thefirst sub bit stream BS0 represents a sequence of variable-bit-numberframes.

Every frame of the first sub bit stream BS0 is designed as follows. Astarting portion of the frame is occupied by the frame header. The frameheader is successively followed by the first sample of thecalculation-result signal Lf+Rf, the first sample of thecalculation-result signal Lf−Rf, a set of the (Lf+Rf)-relatedpredictor-selection flags, a set of the (Lf−Rf)-relatedpredictor-selection flags, a set of the (Lf+Rf)-related bit-numberflags, and a set of the (Lf−Rf)-related bit-number flags. A set of the(Lf−Rf)-related bit-number flags is successively followed by a1-frame-corresponding set of the packing-resultant samples of theselected (Lf+Rf)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (Lf−Rf)-related prediction-error signal. Since pluralsub-frames compose one frame and the number of bits of everypacking-resultant sample varies from sub-frame to sub-frame, a1-frame-corresponding set of the packing-resultant samples of theselected (Lf+Rf)-related prediction-error signal has a variable bitnumber. Also, a 1-frame-corresponding set of the packing-resultantsamples of the selected (Lf−Rf)-related prediction-error signal has avariable bit number.

The formatting circuit 19 receives the signal representing thecoefficient “a”. The formatting circuit 19 receives the frame-headersignal from the signal generator 20 for every frame. The formattingcircuit 19 receives the first sample of the calculation-result signalC−(Ls+Rs)/2, the first sample of the calculation-result signal Ls+Rs,the first sample of the calculation-result signal Ls−Rs, and the firstsample of the calculation-result signal Lfe−a×C from the buffer 10 forevery frame. The formatting circuit 19 receives the(C−(Ls+Rs)/2)-related predictor-selection flag, the (Ls+Rs)-relatedpredictor-selection flag, the (Ls−Rs)-related predictor-selection flag,and the (Lfe−a×C)-related predictor-selection flag from the selectionsignal/DTS generator 17 for every sub-frame. The formatting circuit 19receives the (C−(Ls+Rs)/2)-related bit-number flag, the (Ls+Rs)-relatedbit-number flag, the (Ls−Rs)-related bit-number flag, and the(Lfe−a×C)-related bit-number flag from the selection signal/DTSgenerator 17 for every sub-frame. The formatting circuit 19 receivesevery packing-resultant sample of the selected (C−(Ls+Rs)/2)-relatedprediction-error signal, every packing-resultant sample of the selected(Ls+Rs)-related prediction-error signal, every packing-resultant sampleof the selected (Ls−Rs)-related prediction-error signal, and everypacking-resultant sample of the selected (Lfe−a×C)-relatedprediction-error signal from the packing circuit 18. The formattingcircuit 19 multiplexes the received signals and flags into a second subbit stream BS1 on a time sharing basis. The second sub bit stream BS1represents a sequence of variable-bit-number frames.

Every frame of the second sub bit stream BS1 is designed as follows. Astarting portion of the frame is occupied by the frame header. The frameheader is successively followed by the signal of the coefficient “a”,the first sample of the calculation-result signal C−(Ls+Rs)/2, the firstsample of the calculation-result signal Ls+Rs, the first sample of thecalculation-result signal Ls−Rs, the first sample of thecalculation-result signal Lfe−a×C, a set of the (C−(Ls+Rs)/2)-relatedpredictor-selection flags, a set of the (Ls+Rs)-relatedpredictor-selection flags, a set of the (Ls−Rs)-relatedpredictor-selection flags, a set of the (Lfe−a×C)-relatedpredictor-selection flags, a set of the (C−(Ls+Rs)/2)-related bit-numberflags, a set of the (Ls+Rs)-related bit-number flags, a set of the(Ls−Rs)-related bit-number flags, and a set of the (Lfe−a×C)-relatedbit-number flags. A set of the (Lfe−a×C)-related bit-number flags issuccessively followed by a 1-frame-corresponding set of thepacking-resultant samples of the selected (C−(Ls+Rs)/2)-relatedprediction-error signal, a 1-frame-corresponding set of thepacking-resultant samples of the selected (Ls+Rs)-relatedprediction-error signal, a 1-frame-corresponding set of thepacking-resultant samples of the selected (Ls−Rs)-relatedprediction-error signal, and a 1-frame-corresponding set of thepacking-resultant samples of the selected (Lfe−a×C)-relatedprediction-error signal. Since plural sub-frames compose one frame andthe number of bits of every packing-resultant sample varies fromsub-frame to sub-frame, a 1-frame-corresponding set of thepacking-resultant samples of the selected (C−(Ls+Rs)/2)-relatedprediction-error signal has a variable bit number. Also, a1-frame-corresponding set of the packing-resultant samples of theselected (Ls+Rs)-related prediction-error signal has a variable bitnumber. In addition, a 1-frame-corresponding set of thepacking-resultant samples of the selected (Ls−Rs)-relatedprediction-error signal has a variable bit number. Furthermore, a1-frame-corresponding set of the packing-resultant samples of theselected (Lfe−a×C)-related prediction-error signal has a variable bitnumber.

A signal representing the predetermined sampling frequency fs is appliedto the formatting circuit 19 from an external. A signal representing thepredetermined quantization bit number Qb is applied to the formattingcircuit 19 from an external.

The selection signal/DTS generator 17 produces a decoding time stamp (aDTS) in response to, for example, the previously-mentioned bit-numberflags. The DTS denotes every desired timing at which segments of datastreams should be read out from an input buffer in a decoder side. Theselection signal/DTS generator 17 informs the formatting circuit 19 ofthe DTS.

A PIS generator 17A produces a presentation time stamp (a PTS). The PTSdenotes every desired timing at which audio data should be read out froman output buffer in a decoder side. The PTS generator 17A informs theformatting circuit 19 of the PTS.

The DVD-audio encoder in the formatting circuit 19 provides operation ofthe formatting circuit 19 which will be indicated below. The formattingcircuit 19 combines the first sub bit stream BS0, the second sub bitstream BS1, the signal of the DTS, the signal of the PTS, the signal ofthe predetermined sampling frequency fs, and the signal of thepredetermined quantization bit number Qb into a main bit stream being aDVD-audio-format signal. The formatting circuit 19 outputs the main bitstream, that is, the DVD-audio-format signal, to the transmission line250 (see FIG. 1).

The DVD-audio-format signal generated by the formatting circuit 19 has astream of packs including audio packs. As shown in FIG. 4, each audiopack has a sequence of 4-byte pack start information, 6-byte SCR (systemclock reference) information, 3-byte mux rate information, 1-bytestuffing data, and 2,034-byte packet-form user data. Thus, each audiopack has 2,048 bytes. In each audio pack, pack start information, SCRinformation, mux rate information, and stuffing data compose a 14-bytepack header. SCR information in each audio pack serves as a time stamp.In each audio pack, 2,034-byte packet-form user data contains portionsof the first sub bit stream BS0 and portions of the second sub bitstream BS1.

A time stamp (SCR information) in a first audio pack among audio packsrelated to one title is set to “1”. Time stamps in second and lateraudio packs related to the same title are set to serial numbers “2”,“3”, “4”, . . . , respectively. The serially-numbered time stamps makeit possible to manage times of audio packs related to the same title.

As shown in FIG. 5, one audio pack has a 14-byte or 19-byte pack headerand an audio packet. The pack header is followed by the audio packet.The audio packet has a sequence of a packet header, a private header,and audio data (PCM audio data). Preferably, the packet header has 19bytes. The 10-th byte to the 14-th byte in the packet header are loadedwith the PTS. The 15-th byte to the 19-th byte in the packet header areloaded with the DTS. The packet header may have 14 bytes or anothergiven number of bytes. The audio data has 1 byte to 2,015 bytes. Theaudio data contains portions of the first sub bit stream BS0 andportions of the second sub bit stream BS1.

As shown in FIG. 5, the private header has a sequence of 1-byte substream ID (identification) information, 2-byte information of anUPC/EAN-ISRC (Universal Product Code/European ArticleNumber-International Standard Recording Code) number and UPC/EAN-ISRCdata, 1-byte information of the private header length, a 2-byte firstaccess unit pointer, 4-byte audio data information ADI, and 0 to 7stuffing bytes.

The 1-st byte of the audio data information ADI represents a forwardaccess unit search pointer to allow a search for a 1-second-after accessunit. The 2-nd byte of the audio data information ADI represents abackward access unit search pointer to allow a search for a1-second-before access unit.

As shown in FIG. 6, audio data in one audio packet has PPCM sync signalsand sub packets. The PPCM sync signals alternate with the sub packets.Each PPCM sync signal and a following sub packet compose a PPCM accessunit. The sub packet in the first PPCM access unit has a sequence of adirectory signal, a portion of the first sub bit stream BS0, a CRC(cyclic redundancy check) signal, a portion of the second sub bit streamBS1, a CRC signal, and an extra information piece. The sub packet ineach of the second and later PPCM access units has a sequence of arestart header, a portion of the first sub bit stream BS0, a CRC signal,a restart header, a portion of the second sub bit stream BS1, a CRCsignal, and an extra information piece.

Each PPCM sync signal contains an information piece representing thenumber of samples per packet, an information piece representing a datarate, an information piece representing the predetermined samplingfrequency fs, an information piece representing the predeterminedquantization bit number Qb, an information piece representing channelassignment. The number of samples per packet is set to 40, 80, or 160 inaccordance with the predetermined sampling frequency fs. The informationpiece representing the data rate is set to an identifier of “0” whichdenotes that audio data in the related sub packet is compressed data(compression-resultant data) with a variable bit rate.

As shown in FIG. 7, the decoder 130 includes a deformatting circuit 21which receives the main bit stream, that is, the DVD-audio-formatsignal, from the transmission line 250 (see FIG. 1). The deformattingcircuit 21 includes a DVD-audio decoder and a demultiplexer. TheDVD-audio decoder is followed by the demultiplexer. The DVD-audiodecoder provides operation of the deformatting circuit 21 which will beindicated below.

The deformatting circuit 21 first separates an audio packet from everyaudio pack, and separates the first sub bit stream BS0 and the secondsub bit stream BS1 from the main bit stream (the DVD-audio-formatsignal). The deformatting circuit 21 separates the SCR information andthe DTS signal from the main bit stream. The deformatting circuit 21outputs the SCR information and the DTS signal to the input buffer 22 a.The deformatting circuit 21 separates the PTS signal from the main bitstream. The deformatting circuit 21 outputs the PTS signal to an outputbuffer (an output memory) 55. The deformatting circuit 21 separates thedata rate information (the data rate identifier) from the main bitstream. The deformatting circuit 21 outputs the data rate information toa controller 50. The deformatting circuit 21 separates the forward andbackward access unit search pointers from the main bit stream. Thedeformatting circuit 21 informs the controller 50 of the forward andbackward access unit pointers. The deformatting circuit 21 separates thesignal of the predetermined sampling frequency fs and the signal of thepredetermined quantization bit number Qb from the main bit stream. Thedeformatting circuit 21 outputs the signal of the predetermined samplingfrequency fs and the predetermined bit number Qb to a digital-to-analog(D/A) converter 52.

The demultiplexer in the deformatting circuit 21 provides operation ofthe deformatting circuit 21 which will be indicated below. Thedeformatting circuit 21 detects every frame header in the first sub bitstream BS0. For every frame, the deformatting circuit 21 demultiplexes,in response to the detected frame header, the first sub bit stream BS0into the first sample of the calculation-result signal Lf+Rf, the firstsample of the calculation-result signal Lf−Rf, a set of the(Lf+Rf)-related predictor-selection flags, a set of the (Lf−Rf)-relatedpredictor-selection flags, a set of the (Lf+Rf)-related bit-numberflags, a set of the (Lf−Rf)-related bit-number flags, a1-frame-corresponding set of the packing-resultant samples of theselected (Lf+Rf)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (Lf−Rf)-related prediction-error signal.

The deformatting circuit 21 outputs the first sample of thecalculation-result signal Lf+Rf to a prediction circuit 24D1 for everyframe. The deformatting circuit 21 outputs every (Lf+Rf)-relatedpredictor-selection flag to the prediction circuit 24D1. Thedeformatting circuit 21 outputs the first sample of thecalculation-result signal Lf−Rf to a prediction circuit 24D2 for everyframe. The deformatting circuit 21 outputs every (Lf−Rf)-relatedpredictor-selection flag to the prediction circuit 24D2. Thedeformatting circuit 21 outputs every (Lf+Rf)-related bit-number flagand every (Lf−Rf)-related bit-number flag to a de-packing circuit 22.The deformatting circuit 21 outputs every packing-resultant sample ofthe selected (Lf+Rf)-related prediction-error signal, and everypacking-resultant sample of the selected (Lf−Rf)-relatedprediction-error signal to the input buffer 22 a.

The deformatting circuit 21 detects every frame header in the second subbit stream BS1. For every frame, the deformatting circuit 21demultiplexes, in response to the detected frame header, the second subbit stream BS1 into the signal of the coefficient “a”, the first sampleof the calculation-result signal C−(Ls+Rs)/2, the first sample of thecalculation-result signal Ls+Rs, the first sample of thecalculation-result signal Ls−Rs, the first sample of thecalculation-result signal Lfe−a×C, a set of the (C−(Ls+Rs)/2)-relatedpredictor-selection flags, a set of the (Ls+Rs)-relatedpredictor-selection flags, a set of the (Ls−Rs)-relatedpredictor-selection flags, a set of the (Lfe−a×C)-relatedpredictor-selection flags, a set of the (C−(Ls+Rs)/2)-related bit-numberflags, a set of the (Ls+Rs)-related bit-number flags, a set of the(Ls−Rs)-related bit-number flags, a set of the (Lfe−a×C)-relatedbit-number flags, a 1-frame-corresponding set of the packing-resultantsamples of the selected (C−(Ls+Rs)/2)-related prediction-error signal, a1-frame-corresponding set of the packing-resultant samples of theselected (Ls+Rs)-related prediction-error signal, a1-frame-corresponding set of the packing-resultant samples of theselected (Ls−Rs)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (Lfe−a×C)-related prediction-error signal.

The deformatting circuit 21 outputs the signal of the coefficient “a” tothe mix and matrix circuit 140 (see FIG. 1). The deformatting circuit 21outputs the first sample of the calculation-result signal C−(Ls+Rs)/2 toa prediction circuit 24D3 for every frame. The deformatting circuit 21outputs every (C−(Ls+Rs)/2)-related predictor-selection flag to theprediction circuit 24D3. The deformatting circuit 21 outputs the firstsample of the calculation-result signal Ls+Rs to a prediction circuit24D4 for every frame. The deformatting circuit 21 outputs every(Ls+Rs)-related predictor-selection flag to the prediction circuit 24D4.The deformatting circuit 21 outputs the first sample of thecalculation-result signal Ls−Rs to a prediction circuit 24D5 for everyframe. The deformatting circuit 21 outputs every (Ls−Rs)-relatedpredictor-selection flag to the prediction circuit 24D5. Thedeformatting circuit 21 outputs the first sample of thecalculation-result signal Lfe−a×C to a prediction circuit 24D6 for everyframe. The deformatting circuit 21 outputs every (Lfe−a×C)-relatedpredictor-selection flag to the prediction circuit 24D6. Thedeformatting circuit 21 outputs every (C−(Ls+Rs)/2)-related bit-numberflag, every (Ls+Rs)-related bit-number flag, every (Ls−Rs)-relatedbit-number flag, and every (Lfe−a×C)-related bit-number flag to thede-packing circuit 22. The deformatting circuit 21 outputs everypacking-resultant sample of the selected (C−(Ls+Rs)/2)-relatedprediction-error signal, every packing-resultant sample of the selected(Ls+Rs)-related prediction-error signal, every packing-resultant sampleof the selected (Ls−Rs)-related prediction-error signal, and everypacking-resultant sample of the selected (Lfe−a×C)-relatedprediction-error signal to the input buffer 22 a.

As shown in FIG. 8, the selected (Lf+Rf)-related prediction-errorsignal, the selected (Lf−Rf)-related prediction-error signal, theselected (C−(Ls+Rs)/2)-related prediction-error signal, the selected(Ls+Rs)-related prediction-error signal, the selected (Ls−Rs)-relatedprediction-error signal, and the selected (Lfe−a×C)-relatedprediction-error signal are stored into the input buffer 22 a inresponse to the SCR information for every access unit. As shown in FIGS.9 and 10, access units are variable in bit length. As shown in FIG. 8,the selected (Lf+Rf)-related prediction-error signal, the selected(Lf−Rf)-related prediction-error signal, the selected(C−(Ls+Rs)/2)-related prediction-error signal, the selected(Ls+Rs)-related prediction-error signal, the selected (Ls−Rs)-relatedprediction-error signal, and the selected (Lfe−a×C)-relatedprediction-error signal are read out from the input buffer 22 a inresponse to the DTS signal before being fed to the de-packing circuit22. The input buffer 22 a serves as a FIFO memory.

For every sub-frame, the de-packing circuit 22 implements the unpacking(expansion) of the packing-resultant samples of the selected(Lf+Rf)-related prediction-error signal in response to the(Lf+Rf)-related bit-number flag. The de-packing circuit 22 outputs theresultant (Lf+Rf)-related prediction-error signal to the predictioncircuit 24D1. For every sub-frame, the de-packing circuit 22 implementsthe unpacking (expansion) of the packing-resultant samples of theselected (Lf−Rf)-related prediction-error signal in response to the(Lf−Rf)-related bit-number flag. The de-packing circuit 22 outputs theresultant (Lf−Rf)-related prediction-error signal to the predictioncircuit 24D2. For every sub-frame, the de-packing circuit 22 implementsthe unpacking (expansion) of the packing-resultant samples of theselected (C−(Ls+Rs)/2)-related prediction-error signal in response tothe (C−(Ls+Rs)/2)-related bit-number flag. The de-packing circuit 22outputs the resultant (C−(Ls+Rs)/2)-related prediction-error signal tothe prediction circuit 24D3. For every sub-frame, the de-packing circuit22 implements the unpacking (expansion) of the packing-resultant samplesof the selected (Ls+Rs)-related prediction-error signal in response tothe (Ls+Rs)-related bit-number flag. The de-packing circuit 22 outputsthe resultant (Ls+Rs)-related prediction-error signal to the predictioncircuit 24D4. For every sub-frame, the de-packing circuit 22 implementsthe unpacking (expansion) of the packing-resultant samples of theselected (Ls−Rs)-related prediction-error signal in response to the(Ls−Rs)-related bit-number flag. The de-packing circuit 22 outputs theresultant (Ls−Rs)-related prediction-error signal to the predictioncircuit 24D5. For every sub-frame, the de-packing circuit 22 implementsthe unpacking (expansion) of the packing-resultant samples of theselected (Lfe−a×C)-related prediction-error signal in response to the(Lfe−a×C)-related bit-number flag. The de-packing circuit 22 outputs theresultant (Lfe−a×C)-related prediction-error signal to the predictioncircuit 24D6.

Operation of the prediction circuit 24D1 is inverse with respect tooperation of the prediction circuit 13D1 in the encoder 120 (see FIG.2). The prediction circuit 24D1 includes an adder which receives the(Lf+Rf)-related prediction-error signal. Also, the prediction circuit24D1 includes predictors which have the same characteristics as those ofthe predictors 13 a-1, 13 a-2, . . . , and 13 a-n in the predictioncircuit 13D1, respectively. For every sub-frame, one of the predictorsin the prediction circuit 24D1 is selected in response to the(Lf+Rf)-related predictor-selection flag. Specifically, one of thepredictors is selected which has the same characteristic as theencoder-side predictor used for the sub-frame of interest. The selectedpredictor generates a prediction-result signal in response to an outputsignal of the adder. The selected predictor is enabled to output theprediction-result signal to the adder. The adder combines the(Lf+Rf)-related prediction-error signal and the prediction-result signalinto an (Lf+Rf)-related addition-result signal. The adder outputs the(Lf+Rf)-related addition-result signal to the predictors. At a start ofevery frame, the (Lf+Rf)-related addition-result signal is initializedto the first sample of the calculation-result signal Lf+Rf. Then, the(Lf+Rf)-related addition-result signal is updated sample by sample. Asequence of resultant samples of the (Lf+Rf)-related addition-resultsignal is a sequence of samples of a reproduced signal corresponding tothe calculation-result signal Lf+Rf outputted from the mix and matrixcircuit 110 in the audio signal encoding apparatus 100 (see FIG. 1). Theprediction circuit 24D1 outputs the reproduced calculation-result signalLf+Rf to the output buffer 55.

The prediction circuits 24D2, 24D3, 24D4, 24D5, and 24D6 are similar instructure to the prediction circuit 24D1. The prediction circuits 24D2,24D3, 24D4, 24D5, and 24D6 operate similarly to the operation of theprediction circuit 24D1. The prediction circuit 24D2 reproduces thecalculation-result signal Lf−Rf. The prediction circuit 24D2 outputs thereproduced calculation-result signal Lf−Rf to the output buffer 55. Theprediction circuit 24D3 reproduces the calculation-result signalC−(Ls+Rs)/2. The prediction circuit 24D3 outputs the reproducedcalculation-result signal C−(Ls+Rs)/2 to the output buffer 55. Theprediction circuit 24D4 reproduces the calculation-result signal Ls+Rs.The prediction circuit 24D4 outputs the reproduced calculation-resultsignal Ls+Rs to the output buffer 55. The prediction circuit 24D5reproduces the calculation-result signal Ls−Rs. The prediction circuit24D5 outputs the reproduced calculation-result signal Ls−Rs to theoutput buffer 55. The prediction circuit 24D6 reproduces thecalculation-result signal Lfe−a×C. The prediction circuit 24D6 outputsthe reproduced calculation-result signal Lfe−a×C to the output buffer55.

The reproduced calculation-result signal Lf+Rf, the reproducedcalculation-result signal Lf−Rf, the reproduced calculation-resultsignal C−(Ls+Rs)/2, the reproduced calculation-result signal Ls+Rs, thereproduced calculation-result signal Ls−Rs, and the calculation-resultsignal Lfe−a×C are stored into the output buffer 55. The reproducedcalculation-result signal Lf+Rf, the reproduced calculation-resultsignal Lf−Rf, the reproduced calculation-result signal C−(Ls+Rs)/2, thereproduced calculation-result signal Ls+Rs, the reproducedcalculation-result signal Ls−Rs, and the calculation-result signalLfe−a×C are read out from the output buffer 55 in response to the PTSsignal before being fed to the mix and matrix circuit 140 (see FIG. 1).Accordingly, the reproduced calculation-result signal Lf+Rf, thereproduced calculation-result signal Lf−Rf, the reproducedcalculation-result signal C−(Ls+Rs)/2, the reproduced calculation-resultsignal Ls+Rs, the reproduced calculation-result signal Ls−Rs, and thecalculation-result signal Lfe−a×C are read out from the output buffer 55presentation-unit by presentation-unit. Thus, as shown in FIG. 10,access units are changed into presentation units which are fixed in bitlength.

Operation of a first portion of the mix and matrix circuit 140 isinverse with respect to the operation of the mix and matrix circuit 110in the audio signal encoding apparatus 100. The first portion of the mixand matrix circuit 140 converts a set of the reproducedcalculation-result signal Lf+Rf, the reproduced calculation-resultsignal Lf−Rf, the reproduced calculation-result signal C−(Ls+Rs)/2, thereproduced calculation-result signal Ls+Rs, the reproducedcalculation-result signal Ls−Rs, and the calculation-result signalLfe−a×C into a set of a reproduced left-front digital audio signal Lf, areproduced right-front digital audio signal Rf, a center digital audiosignal C, a reproduced left-surround digital audio signal Ls, areproduced right-surround digital audio signal Rs, and a reproducedlow-frequency-effect digital audio signal Lfe. The first portion of themix and matrix circuit 140 outputs the 6-channel reproduced digitalaudio signals Lf, Rf, C, Ls, Rs, and Lfe to the D/A converter 52 (seeFIG. 7) or an external device (not shown). The mix and matrix circuit140 uses the signal of the coefficient “a” in generating the reproducedlow-frequency-effect digital audio signal Lfe.

A second portion of the mix and matrix circuit 140 includes multipliersand adders designed and connected to mix the 6-channel reproduceddigital audio signals Lf, Rf, C, Ls, Rs, and Lfe into a left-channeldigital audio signal L and a right-channel digital audio signal Raccording to equations as follows.L=m11·Lf+m12·Rf+m13·C+m14·Ls+m15·Rs+m16·LfeR=m21·Lf+m22·Rf+m23·C+m24·Ls+m25·Rs+m26·Lfewhere m11-m16 and m21-m26 denote predetermined mixing coefficients. Thesecond portion of the mix and matrix circuit 140 outputs theleft-channel digital audio signal L and the right-channel digital audiosignal R to the D/A converter 52 (see FIG. 7) or an external device (notshown).

The D/A converter 52 changes the 6-channel reproduced digital audiosignals Lf, Rf, C, Ls, Rs, and Lfe into corresponding 6-channel analogaudio signals in response to the predetermined sampling frequency fs andthe predetermined quantization bit number Qb. The D/A converter 52outputs the 6-channel analog audio signals to external devices (notshown). In addition, the D/A converter 52 changes the left-channeldigital audio signal L and the right-channel digital audio signal R intocorresponding 2-channel analog audio signals in response to the signalof the predetermined sampling frequency fs and the signal of thepredetermined quantization bit number Qb. The D/A converter 52 outputsthe 2-channel analog audio signals to external devices (not shown).

The controller 50 is connected to an operation unit 51. When a commandfor search playback is inputted into the controller 50 via the operationunit 51, the controller 50 acts to implement the playback of data from adesired access unit in response to the forward access unit searchpointer or the backward access unit search pointer.

Preferably, the device 50 controls the de-packing circuit 22 in responseto the data rate identifier. When the data rate identifier denotes thataudio data in the related sub packet is compressed data(compression-resultant data), the controller 50 enables the de-packingcircuit 22 to implement the desired data expansion process.

An fs conversion circuit may precede the mix and matrix circuit 110. Thefs conversion circuit is the same as an fs conversion circuit 109 in asixth embodiment of this invention which will be explained later.

Second Embodiment

A second embodiment of this invention is similar to the first embodimentthereof except for design changes mentioned later.

With reference to FIG. 11, the second embodiment of this inventionincludes a packeting processor 350 which follows the audio signalencoding apparatus 100. The packeting processor 350 encodes the outputsignal of the audio signal encoding apparatus (that is, the main bitstream) into a packet stream. The packeting processor 350 transmits thepacket stream to a communication network (or a communication line) 360.

A de-packeting processor 370 receives the packet stream from thecommunication network 360. The de-packeting processor 370 decodes thepacket stream into the main bit stream. The de-packeting processor 370outputs the main bit stream to the audio signal decoding apparatus 200.

The packeting processor 350 operates in accordance with a controlprogram stored in its internal ROM or another memory. FIG. 12 is aflowchart of a segment of the control program. As shown in FIG. 12, afirst step S41 of the program segment divides the main bit stream intobasic packets each having a predetermined number of bits. A step S42following the step S41 adds headers to the starting ends of the basicpackets to change the basic packets to final packets respectively.Generally, the added headers include destination addresses. A step S43subsequent to the step S42 sequentially transmits the final packets tothe communication network 360.

The de-packeting processor 370 operates in accordance with a controlprogram stored in its internal ROM or another memory. FIG. 13 is aflowchart of a segment of the control program. As shown in FIG. 13, afirst step S51 of the program segment removes headers from receivedpackets. A step S52 following the step S51 recovers the main bit streamfrom the header-less packets. A step S53 subsequent to the step S52stores the recovered main bit stream into a buffer memory provided inthe de-packeting processor 370. The main bit stream is transmitted fromthe buffer memory to the audio signal decoding apparatus 200.

Third Embodiment

A third embodiment of this invention is similar to the first embodimentthereof except for design changes indicated hereinafter. In the thirdembodiment of this invention, an audio signal encoding apparatusincludes a down mixing circuit which converts a set of 6-channel inputdigital audio signals Lf, Rf, C, Ls, Rs, and Lfe into a pair of aleft-channel digital audio signal L and a right-channel digital audiosignal R as the mix and matrix circuit 140 in the first embodiment ofthis invention does. A mix and matrix circuit following the down mixingcircuit converts a set of the digital audio signals L, R, C, Ls, Rs, andLfe into a set of a calculation-result signal L+R, a calculation-resultsignal L−R, a calculation-result signal C−(Ls+Rs)/2, acalculation-result signal Ls+Rs, a calculation-result signal Ls−Rs, anda calculation-result signal Lfe−C. The calculation-result signals L+R,L−R, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−C are encoded as thecalculation-result signals Lf+Rf, Lf−Rf, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, andLfe−a×C are encoded in the first embodiment of this invention.

The calculation-result signals L+R, L−R, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, andLfe−C are reproduced by a decoding process as the calculation-resultsignals Lf+Rf, Lf−Rf, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−a×C arereproduced in the first embodiment of this invention. The left-channeldigital audio signal L is recovered by adding the reproducedcalculation-result signal L+R and the reproduced calculation-resultsignal L−R. The right-channel digital audio signal R is recovered bysubtracting the reproduced calculation-result signal L−R from thereproduced calculation-result signal L+R.

Fourth Embodiment

FIG. 14 shows a fourth embodiment of this invention which is similar tothe first embodiment thereof except for design changes indicatedhereinafter. The fourth embodiment of this invention includes mix andmatrix circuits 110A and 140A instead of the mix and matrix circuits 110and 140 in the first embodiment of this invention.

The mix and matrix circuit 110A includes a down mixing circuit whichconverts a set of 6-channel input digital audio signals Lf, Rf, C, Ls,Rs, and Lfe into a pair of a left-channel digital audio signal L and aright-channel digital audio signal R as the mix and matrix circuit 140in the first embodiment of this invention does. The mix and matrixcircuit 110A outputs the left-channel digital audio signal L and theright-channel digital audio signal R to an encoder 120.

The mix and matrix circuit 110A converts a set of the input digitalaudio signals C, Ls, Rs, and Lfe into a set of a calculation-resultsignal C−(Ls+Rs)/2, a calculation-result signal Ls+Rs, acalculation-result signal Ls−Rs, and a calculation-result signal Lfe−C.The mix and matrix circuit 110A outputs the calculation-result signalsC−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−C to the encoder 120.

The digital audio signals L, R, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−C areencoded by the device 120 as the calculation-result signals Lf+Rf,Lf−Rf, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−a×C are encoded in the firstembodiment of this invention. In this case, the digital audio signals Land R are stored in a portion of the first sub bit steam BS0 shown inFIG. 6, and the other audio signals C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−Care stored in a portion of the second sub bit stream BS1 shown in FIG.6.

In the fourth embodiment of this invention, a decoder 130 reproduces thedigital audio signals L, R, C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−C. Thedecoder 130 outputs the reproduced digital audio signals L, R,C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−C to the mix and matrix circuit 140A.

The mix and matrix circuit 140A converts a set of the reproduced digitalaudio signals C−(Ls+Rs)/2, Ls+Rs, Ls−Rs, and Lfe−C into a set of thereproduced digital audio signals C, Ls, Rs, and Lfe. The mix and matrixcircuit 140A outputs the reproduced digital audio signals C, Ls, Rs, andLfe.

The mix and matrix circuit 140A reproduces the digital audio signals Lfand Rf by suitably combining the reproduced digital audio signals L, R,C, Ls, Rs, and Lfe. The mix and matrix circuit 140A outputs thereproduced digital audio signals Lf and Rf. In addition, the mix andmatrix circuit 140A outputs the reproduced digital audio signals L andR. In this embodiment, if users want to reproduce only the digital audiosignal L and the digital audio signal R without other channels, thesignal processing by the mix and matrix circuit 140A can be simpler.

Fifth Embodiment

A fifth embodiment of this invention is similar to the first embodimentthereof except for design changes indicated hereinafter.

FIG. 15 shows an audio signal encoding apparatus in the fifth embodimentof this invention. The audio signal encoding apparatus of FIG. 15processes 6-channel input digital audio signals Lf, C, Rf, Ls, Rs, andLfe.

The audio signal encoding apparatus of FIG. 15 includes a buffer 10. Thedigital audio signals Lf, C, Rf, Ls, Rs, and Lfe are stored into thebuffer 10 frame by frame. The digital audio signals Lf, C, Rf, Ls, Rs,and Lfe are transmitted from the buffer 10 to each of “m” correlationcircuits 60-1, . . . , and 60-m. For every frame, the first samples ofthe digital audio signals Lf, C, Rf, Ls, Rs, and Lfe are transmittedfrom the buffer 10 to a formatting circuit 19.

Each of the correlation circuits 60-1, . . . , and 60-m converts a setof the digital audio signals Lf, C, Rf, Ls, Rs, and Lfe into a set of 6calculation-result signals by a mixing process. The mixing processes bythe correlation circuits 60-1, . . . , and 60-m are different from eachother.

For example, the 1-st correlation circuit 60-1 converts a set of thedigital audio signals Lf, C, Rf, Ls, Rs, and Lfe into a set of 6calculation-result signals Lf, C−(Ls+Rs)/2, Rf−Lf, Ls−a×Lfe, Rs−b×Rf,and Lfe where “a” and “b” denote fixed or variable coefficients in therange between 0 and 1. For example, the m-th correlation circuit 60-mconverts a set of the digital audio signals Lf, C, Rf, Ls, Rs, and Lfeinto a set of 6 calculation-result signals Lf+Rf, C−Lf, Rf−Lf, Ls−Lf,Rs−Lf, and Lfe−C.

Each of the correlation circuits 60-1, . . . , and 60-m outputs the 6calculation-result signals to 6 different prediction circuitsrespectively. The 6 different prediction circuits are followed by 6buffer and selectors respectively.

For example, the 1-st correlation circuit 60-1 outputs thecalculation-result signals Lf, C−(Ls+Rs)/2, Rf−Lf, Ls−a×Lfe, Rs−b×Rf,and Lfe to prediction circuits 13D1-1, 13D2-1, 13D3-1, 13D4-1, 13D5-1,and 13D6-1 respectively. The prediction circuits 13D1-1, 13D2-1, 13D3-1,13D4-1, 13D5-1, and 13D6-1 are followed by buffer and selectors 14D1-1,14D2-1, 14D3-1, 14D4-1, 14D5-1, and 14D6-1 respectively. For example,the m-th correlation circuit 60-m outputs the calculation-result signalsLf+Rf, C−Lf, Rf−Lf, Ls−Lf, Rs−Lf, and Lfe−C to prediction circuits13D1-m, 13D2-m, 13D3-m, 13D4-m, 13D5-m, and 13D6-m respectively. Theprediction circuits 13D1-m, 13D2-m, 13D3-m, 13D4-m, 13D5-m, and 13D6-mare followed by buffer and selectors 14D1-m, 14D2-m, 14D3-m, 14D4-m,14D5-m, and 14D6-m respectively.

Thus, there are “m” groups each having one correlation circuit, 6prediction circuits, and 6 buffer and selectors. The first predictioncircuits in the respective groups are equal to each other. The secondprediction circuits in the respective groups are equal to each other.The third prediction circuits in the respective groups are equal to eachother. The fourth prediction circuits in the respective groups are equalto each other. The fifth prediction circuits in the respective groupsare equal to each other. The sixth prediction circuits in the respectivegroups are equal to each other.

A selection signal/DTS generator 17E searches the 6 buffer and selectorsin each of the groups for the smallest prediction-error signals. Inaddition, the selection signal/DTS generator 17E calculates the totaldata amount of the smallest prediction-error signals in each of thegroups. The selection signal/DTS generator 17E compares the calculatedtotal data amounts for the respective groups, and decides the minimumdata amount among the calculated total data amounts. The selectionsignal/DTS generator 17E selects one from among the groups whichcorresponds to the decided minimum data amount. The selection signal/DTSgenerator 17E enables the 6 buffer and selectors in the selected groupto output the smallest prediction-error signals to a packing circuit 18.

The selection signal/DTS generator 17E produces a flag representing theselected group. The selection signal/DTS generator 17E outputs theselected-group flag to a formatting circuit 19 as acorrelation-circuit-selection flag.

A signal representing the coefficient “a” is applied to the formattingcircuit 19. A signal representing the coefficient “b” is also applied tothe formatting circuit 19. The formatting circuit 19 multiplexes orcombines the correlation-circuit-selection flag, the signal of thecoefficient “a”, the signal of the coefficient “b”, and other signalsinto a main bit stream.

FIG. 16 shows an audio signal decoding apparatus in the fifth embodimentof this invention. The audio signal decoding apparatus of FIG. 16includes a set 62 of “m” correlation circuits 62-1, . . . , and 62-m. Anoutput buffer 55 outputs 6 reproduced calculation-result signals to eachof the correlation circuits 62-1, . . . , and 62-m. Regarding operation,the correlation circuits 62-1, . . . , and 62-m are inverse with respectto the correlation circuits 60-1, . . . , and 60-m, respectively.

In the audio signal decoding apparatus of FIG. 16, a deformattingcircuit 21 separates the correction-circuit-selection flag, the signalof the coefficient “a”, and the signal of the coefficient “b” from themain bit stream. The deformatting circuit 21 outputs thecorrection-circuit-selection flag, the signal of the coefficient “a”,and the signal of the coefficient “b” to the correlation circuit set 62.

In the correlation circuit set 62, one of the correlation circuits 62-1,. . . , and 62-m is selected in response to thecorrection-circuit-selection flag. The selected correlation circuit62-1, . . . , or 62-m corresponds to the selected correlation circuit60-1, . . . , or 60-m in the audio signal encoding apparatus for thepresent output signals from the output buffer 55. The selectedcorrelation circuit 62-1, . . . , or 62-m converts a set of the 6reproduced calculation-result signals into a set of reproduced digitalaudio signals Lf, C, Rf, Ls, Rs, and Lfe. Only the selected correlationcircuit 62-1, . . . , or 62-m is enabled to output the reproduceddigital audio signals Lf, C, Rf, Ls, Rs, and Lfe.

A down mixing circuit may follow the correlation circuit set 62. In thiscase, the down mixing circuit converts a set of the reproduced digitalaudio signals Lf, Rf, C, Ls, Rs, and Lfe into a pair of a left-channeldigital audio signal L and a right-channel digital audio signal R as themix and matrix circuit 140 in the first embodiment of this inventiondoes.

Sixth Embodiment

A sixth embodiment of this invention is similar to the fourth embodimentthereof except for design changes indicated hereinafter.

FIG. 17 shows an audio signal encoding apparatus in the sixth embodimentof this invention. The audio signal encoding apparatus of FIG. 17includes an fs conversion circuit 109 receiving input digital audiosignals C, Ls, Rs, and Lfe. Input digital audio signals Lf and Rf aredirectly fed to the mix and matrix circuit 110A. The fs conversioncircuit 109 equalizes the sampling frequencies of the input digitalaudio signals C, Ls, Rs, and Lfe to a predetermined frequency.Preferably, the predetermined frequency is equal to the highestfrequency among the sampling frequencies of the input digital audiosignals C, Ls, Rs, and Lfe. The fs conversion circuit 109 outputs theconversion-resultant digital audio signals C, Ls, Rs, and Lfe to the mixand matrix circuit 110A. Accordingly, the mix and matrix circuit 110Aprocesses a set of the input digital audio signals Lf and Rf, and theconversion-resultant digital audio signals C, Ls, Rs, and Lfe outputtedfrom the fs conversion circuit 109.

The fs conversion circuit 109 enables the mix and matrix circuit 110A tosuitably operate even in the case where the input digital audio signalsC, Ls, Rs, and Lfe have different sampling frequencies.

Seventh Embodiment

A seventh embodiment of this invention is similar to the firstembodiment thereof except for design changes indicated hereinafter.

FIG. 18 shows a structure of an audio packet used in the seventhembodiment of this invention. As shown in FIG. 18, audio data in oneaudio packet has PPCM sync signals and sub packets. The PPCM syncsignals alternate with the sub packets. Each PPCM sync signal and afollowing sub packet compose a PPCM access unit. The sub packet in thefirst PPCM access unit has a sequence of a directory signal, a portionof the sub bit stream BS0, a CRC (cyclic redundancy check) signal, andan extra information piece. Thus, the sub packet in the first PPCMaccess unit is devoid of a portion of the sub bit stream BS1 (see FIG.6). The sub packet in each of the second and later PPCM access units hasa sequence of a restart header, a portion of the sub bit stream BS0, aCRC signal, and an extra information piece. Thus, the sub packet in eachof the second and later PPCM is devoid of a portion of the sub bitstream BS1 (see FIG. 6).

The digital audio signals L and R are placed and in the sub bit streamBS0 while other channel signals are not placed therein.

1. An audio signal encoding apparatus comprising: means for convertingfirst multiple-channel digital audio signals into audio signals ofstereophonic 2 channels through down mixing; means for implementingmatrix operation among the first multiple-channel digital audio signalsto generate second multiple-channel audio signals correlating with eachother, the first multiple-channel digital audio signals relating to asampling frequency and a quantization bit number, the secondmultiple-channel audio signals lacking 2 channels corresponding to thestereophonic 2 channels; means for compressing the stereophonic2-channel audio signals and the second multiple-channel digital audiosignals into compression-resultant multiple-channel signalsrespectively, the compression-resultant multiple-channel signalsrelating to a smallest prediction-error basis lossless compression; andmeans for formatting the compression-resultant multiple-channel signalsinto a formatting-resultant signal, the formatting-resultant signalcontaining an access unit composed of a sub packet and a syncinformation portion, the sub packet containing at least portions of thecompression-resultant multiple-channel signals, the sync informationportion containing the signal representative of the sampling frequencyand the signal representative of the quantization bit number, whereinsaid access unit is of variable length and said compression-resultantmultiple-channel signals are compressed with a variable bit rate.
 2. Anaudio signal encoding apparatus as recited in claim 1, furthercomprising means for formatting an audio packet into an audio pack, theaudio packet containing said formatting-resultant signal.
 3. An audiosignal decoding apparatus for decoding an input audio signal intooriginal multiple-channel digital audio signals, wherein the input audiosignal has been generated by an audio signal encoding apparatuscomprising 1) means for converting first multiple-channel digital audiosignals into audio signals of stereophonic 2 channels through downmixing; 2) means for implementing matrix operation among the firstmultiple-channel digital audio signals to generate secondmultiple-channel audio signals correlating with each other, the firstmultiple-channel digital audio signals relating to a sampling-frequencyand a quantization bit number, the second multiple-channel audio signalslacking 2channels corresponding to the stereophonic 2 channels; 3) meansfor compressing the second multiple-channel audio signals intocompression-resultant multiple-channel signals respectively, thecompression-resultant multiple-channel signals relating to asmallest-prediction-error basis lossless compression; and 4) means forformatting the compression-resultant multiple-channel signals into aformatting-resultant signal, the formatting-resultant signal containingan access unit composed of a sub packet and a sync information portion,the sub packet containing at least portions of the compression-resultantmultiple-channel signals, the sync information portion containing thesignal representative of the sampling frequency and the signalrepresentative of the quantization bit number, wherein said access unitis of variable length and said compression-resultant multiple-channelsignals are compressed with a variable bit rate; the audio signaldecoding apparatus comprising: means for separating aformatting-resultant signal into an access unit composed of a sub packetand a sync information portion, wherein said access unit is of variablelength; means for extracting compression-resultant multiple-channelsignals from the sub packet of the access unit; means for expanding theextracted compression-resultant multiple-channel signals intomultiple-channel digital audio signals respectively, wherein saidcompression-resultant multiple-channel signals are compressed with avariable bit rate; means for extracting a signal representative of asampling frequency and a signal representative of a quantization bitnumber from the sync information portion; and means for converting themultiple-channel digital audio signals into analog audio signals inresponse to the signal representative of the sampling frequency and thesignal representative of the quantization bit number, wherein the analogaudio signals are at least one of a set of 2-channel analog audiosignals and a set of multiple-channel analog audio signals.
 4. An audiosignal decoding apparatus as recited in claim 3, further comprisingmeans for separating an audio packet from an audio pack, the audiopacket containing said formatting-resultant signal.